1. Field of the Invention
The present invention relates to a method for producing display devices, which includes a step of forming a patterned film by vapor deposition through a mask corresponding to a plurality of pixels arranged in an array of columns and rows.
2. Description of the Related Art
The display device having organic electroluminescence elements arranged and formed therein is usually produced by vapor deposition, which permits organic light-emitting materials corresponding to RGB colors to be deposited on a substrate through a metal mask having a plurality of apertures corresponding to pixels.
An example of mask vapor deposition is shown in FIG. 9 (perspective view) and FIG. 10 (side view). The illustrated mask deposition is intended to form a uniform film on a large substrate. It employs linear evaporation sources 1, each having a straight vapor outlet. Above the linear evaporation sources 1 is placed a vapor deposition mask 3, on which is closely placed a substrate 5. The mask 3 and the substrate 5 are moved relative to the linear evaporation sources 1 in the direction v perpendicular to the lengthwise direction L of the linear evaporation sources 1. During their movement, the deposition material dm evaporates from the linear evaporation sources 1 and passes through the apertures 3a in the mask 3 and deposits at each pixel px on the substrate 5. Thus there is obtained a patterned layer of electroluminescence 7.
The foregoing method usually needs a baffle 9 between the adjacent linear evaporation sources 1. This baffle 9 limits the angle of evaporation and prevents the mixing of the deposition materials evaporating from adjacent linear evaporation sources 1. Each evaporation source 1 is held between two baffles 9, so that there are two baffles 9 between adjacent evaporation sources 2. Incidentally, the deposition material dm evaporating from the linear evaporation source 1 does not deposit uniformly on the substrate. In other words, deposition varies in the lengthwise direction L of the linear evaporation source 1 on account of variation in the angle of evaporation with respect to the substrate 5, as shown in FIG. 10. As the result, the thickness of the deposited film varies across the pixel px on the substrate 5. The deposited film in the effective region a1 in the pixel (in the lengthwise direction L) is thick enough to work satisfactorily, but the deposited film gradually decreases in thickness on moving toward the edges, so that the deposited film in the marginal region a2 in the pixel does not work satisfactorily, as shown in FIG. 11.
The vapor deposition may be accomplished by arranging the rectangular pixels such that their long sides are parallel to the lengthwise direction L of the linear evaporation source 1, as shown in FIG. 9. The deposited film formed in this manner has the wide marginal regions a2 at both edges along the short side of the pixel px, as shown in FIG. 12A. The area of the marginal region a2 in the pixel px is relatively small. Alternatively, the vapor deposition may also be accomplished by arranging the rectangular pixels such that their short sides are parallel to the lengthwise direction L of the linear evaporation source 1. In this case, as shown in FIG. 12B, the deposited film has the marginal regions a2 at both edges along the long sides of the pixel px. The area of the marginal region a2 in the pixel px is larger than that shown in FIG. 12A. See Japanese Patent Laid-Open No. 2003-17256.